The Role of D2D Communications in Public Safety: A
Networking Perspective
Dr. Leonardo Goratti
(Supported by Dr. Tinku Rasheed)
Outline
•Few Basic Facts
•Current Status for Public Safety
•D2D Communications
•Proposed D2D Protocol
•Analysis
•Results
•Conclusions
Few basic Facts – 1
6.8 billion smartphone
subscriptions by Q1
2014
Source: Ericsson Mobility Report, June 2014
Few Basic Facts – 2 Avalanche of
Massive growth in
Large diversity of
Traffic Volume
Connected
Devices
Use cases
&
Requirements
Further expansion of
mobile broadband
“Communicating machines”
Device-to-Device
Communications
Additional traffic due to
communicating machines
“1000x in ten years”
Car-to-Car Comm.
“50 billion devices in 2020”
New requirements and
characteristics due to
communicating machines
Source: A. Osseiran, “Toward a 5G Mobile & Wireless System Concept” FIA Athens March 2014
Few basic facts – 3
1G
2G
2.4 kbit/s
40 kbit/s
per channel
3G
384 kbit/s
4G
300 Mbit/s
5G
What is the Situation for
the Public Safety
Community?
Current Status for Public Safety – 1
•Public protection and Disaster Relief
Organizations (PPDR) intervene in the
aftermath of a crisis and include police forces,
fire fighters, medical aid (e.g. 911 in the USA
or 112 in Europe).
•Professional Mobile radio (PMR) networks
provide communications for PPDR users
Crisis scenarios
Special events
•TETRA, TETRAPOL, P25
Current Status for Public Safety– 2
• PPDR organizations are doing a slow transition to
TETRA in Europe (still rely on analogue
communications in some cases)
•TETRA is similar to GSM technology
Low Data Rate
TDMA-based
Excellent for Group calls (one-to-many), Direct
calls (one-to-one), Message dispatching
DMO of TETRA is essentially D2D
•Major drawback: PPDR organization do not exploit
cutting edge technologies!
Current Status for Public Safety – 3
Current Status for Public Safety – 4
Mobile Communications
Fixed-line Communications
■ Carriers restricted voice traffic by as much as 70 to 95
■ Carriers restricted phone traffic by as much as 80 to
90 percent.*
* There was 4 to 9 times the normal volume of traffic (NTT East.)
Max. outgoing traffic restrictions
percent.*
■ Packet traffic, however, was either not restricted or
restricted at a lower rate (0 to 30 percent) than voice traffic.
* There was 50 to 60 times the normal volume of traffic (DoCoMo).
Max. outgoing traffic restrictions
100%
80%
60%
95%
90%
70%
40%
20%
0%
30%
0%
0%
voice packet voice packet voice packet
Current Status for Public Safety – 5
Need to Move to Mobile Broadband
Migration
D2D Communications
D2D Communications – General View
•Device-to-Device (D2D) is a recent terminology
adopted by 3GPP meaning direct communications
between UEs in 4G technology (licensed bands)
•Emerging D2D communications are expected to
share the same resources with cellular system
•D2D is supposed to be an access or link-layer
technology proposed also for M2M
•D2D is not the first historical attempt to enable
devices with direct communications
•Bluetooth, UWB, mmWave Communications, and
WiFi Direct are some of these examples
D2D Communications – 3GPP
•3GPP studies D2D as part of the wider
concept of Proximity Services (ProSe)
•D2D communication is defined as the
communication between two UEs in physical
proximity using LTE air interface to set up a
direct link without routing via base station
and possibly core network.
•In Rel. 12 3GPP considered ProSe D2D and
isolation conditions for public safety
•More is expected in 3GPP Rel. 13
D2D Communications – General View
•Carriers are not completely in favor of D2D:
interference problems and billing
•The use of D2D has to be distinguished for
commercial and non-commercial domains
•D2D can be established with and without
supervision of an evolved Node B (eNB)
•Several challenges to be solved
–When to start D2D?
– What resources for D2D?
–Which protocol for D2D?
Different D2D usage cases
D2D Communications – Use Cases
Local voice service
UE as a gateway to sensor networks
Local data service
UE cooperative relay
Source: Lei<Lei
LeiLei,
et Zhangdui
al. “Operator
Controlled
Communications
in LTE-Advanced
Zhong, Chuang
Lin andDevice-to-Device
Xuemin (Sherman) Shen,
”Operator Controlled Device-to-Device
Communication in
LTE-Advanced
Networks,”
IEEE Wireless Communications,
Networks” IEEE
Wireless
Communications,
June 2012. June 2012>
D2D Communications – FP7
ABSOLUTE (www.absolute-project.eu)
D2D
scenarios 1
D2D
scenarios 3
D2D
scenarios 2
D2D Communications – Public Safety
•D2D communications for PPDR organizations
Range extension
Relieve lack of resources or network failures
•Guarantee voice services
D2D communications
exploit the physical
Group calls (one-to-many)
proximity of
Direct calls (one-to-one)
professional user
Fast call setup time: fewequipments
milliseconds with LTE-A
Message dispatching
•Many new ones
High-definition video,
Social networking, location augmentation, MTC, location-based
services, and fast file transfer
D2D Communications – Functions
•Discovery of peers
•Devices synchronization
•Protocols for establishing direct links
•Resources allocation
•Different levels of network involvement
Network controlled
Loosely network controlled
No network controlled: ad-hoc fashion
D2D
Communications
–
Peers
Different peer discovery techniques
Discovery
A priori case – broadcasting
A priori case – registration
posteriori case – a token
posteriori case – IP address analysis
<G. Fodor, E. Dahlman, G. Mildh, S. Parkvall, N. Reider, G. Miklós, and Z. Turányi, Ericsson Research, “Design Source: G. Fodor, etaspects
al. “Design
Aspects
of Network communications,”
Assisted Device-to-Device
Communications,”
of network
assisted odevice-to-device
IEEE Cm munications
Magazine, March 2012>
IEEE Communications Magazine, March 2012.
Proposed D2D protocol
Proposed D2D Protocol
•First pillar
Cellular uplink resources for D2D
UEs can Tx/Rx in uplink
Reduce harmful interference in downlink
•Second pillar
Reuse existing PUCCH regions of PRACH allocations
New one could be defined (reserved PRACH, R-PRACH)
Uplink structure known to the UEs
•Third pillar
Allow some modifications to have new PRACHs for data reservation
PUSCH for data exchange in D2D fashion
Proposed D2D Protocol – UEs in
Isolation
•Time of Interruption (ToI): time the A-eNB is
unavailable
•One UE broadcasts direct beacons (D-Beacons)
•Beaconing device (b-UE): the UE of the team leader
•D-Beacons for peer discovery and local synch
•PUCCH: D-Beacons and association responses
•PRACH: association requests to the b-UE
•Reserved PRACH: D2D links reservations (Req. +
Resp.)
•PUSCH: used for D2D data exchange
Proposed D2D Protocol – UEs in
Isolation
•D-Beacon interval: multiples of LTE radio frame (10 ms)
•The D2D network is vanished as soon as connectivity with
the eNB is recovered
If UEs can rely on “two different receivers” they can
keep monitoring the downlink frequency of the eNB
If only one receiving chain: every N D-beacon intervals
UEs should skip D2D to listen to the downlink
•Role of the b-UE can be rotated among UEs to save energy
•D2D links established in P2P with no supervision of the bUE
Autonomous Network formation!
Proposed D2D Protocol – UEs in
Isolation
D-beacon interval
NRB-1
t
(UL)
PUCCH (used by the b-UE)
PRACH
PRACH
(reserved)
PRACH
PRACH
(reserved)
PUSCH
f
PUCCH
Structure of the proposed D2D framework
12 subcarriers
NRB0(UL)
Proposed D2D Protocol – UEs in
Isolation
•D2D network association
Four-way handshake as in standard LTE
UEs select a preamble in contention mode
collisions
The b-UE replies over the PUCCH (no collisions)
UEs which have assigned a network identifier could reuse
that
To facilitate subsequent network operations single UEs could
reuse the selected preamble or
Use a unique preamble sequence for the whole D2D network
Used in the analysis
Proposed D2D Protocol – UEs in
Network Coverage
D2D protocol as before but prior to eNB
authorization and reasoning
Cognitiv
e
Process
Locatio
n
Awaren
ess
4G
Connectivit
y
Tx.
Paramet
er
Setting
eNB
Supervi
sion
Analysis
Analysis – 1
•In D2D communications relying on “Reuse 1” 4G cellular
technology Interference is a major problem
•We rely on the theory of Spatial Point Processes
•Point Processes are useful to model location of
transmitters that follow specific spatial patterns(locations),
adding fading and shadowing
•Early attempts to use Point Processes in wireless
[1] E. Sousa and J. Silvester, “Optimum Transmission Ranges in a Direct-Sequence Spread-Spectrum Multihop Packet
Radio Network,” IEEE J. on Selected Areas in Communications, vol.. 8. no. 5. June 1900
[2] R. Nelson and L. Kleinrock, “The Spatial Capacity of a Slo’tted ALOHA Multihop Packet Radio Network with
Capture,” IEEE Trans. on Commun., vol. COM-32, no. 6, June 1984
[3] J. Ilok and D. Hatzinakos, “Analytic Alpha-Stable Noise Modeling in a Poisson Field of Interferers or Scatterers,”
IEEE trans. on Signal Processing, vol. 46, no. 6, June 1998.
•[3] established that a homogeneous Poisson Point Process
is equivalent to a Poisson process on the line with intensity
πλ
Analysis – 2
•Definition1: A point Process (PP) is a random
variable taking values in the space N
•A PP is denoted by Φ, whereas an
instantiation of the process is denoted by
 ( A)  1A ( x), where 1 is the indicator function
A
x
•In a region AϵRd the number of points of a PP
is N(A), or intensity measure
•A PP can be finite (N(A) for any bounded
region) and simple (xi≠xj for all i≠j)
D.J. Daley, D. Vere-Jones , An introduction to the theory of point processes, Vol 1 and 2,
Analysis – 3
•A Poisson PP (PPP) is a special case of great
importance
PPP is simple,
PPP is stationary and isotropic
Points in space are independently distributed
Number of points in independent sets are also
independent

 A
P{k nodes in } 
k
s
k!
e
 s A
Analysis – 4
•Palm distribution theory formalize the concept of a typical
point for PPs
•Slivnyak’s Theorem: For a stationary PPP holds that
Pr{ has property Y | o}  Pr{  {o}has property Y}
•Campbell Theorem: For a stationary PPP of intensity λ and a
non-negative measurable function f(x) E (  f ( x))    f ( x)dx
x
R
•Laplace functional: For a stationary PPP of intensity λ and a
function f(x) with values in [0,1]
2





L ( f )  E  f ( x)  exp    (1  f ( x)) dx 


2
 x

 R

•For Cluster PPs Lλ is similar but more complex
•Cluster Processes are important for D2D
Analysis – 5
I ( y )   Ptx g xl y  x
x
r0
r2
r3
r1
Reference
UE
L( s)  E  exp(  sPti g i ri )

i
•By Slivnyak’s theorem we
can select the reference
(typical) receiver placed in
any point
•By the stationary and
isotropy of PPPs it’s
enough to consider the
distance y-x rather than
specific points

yx r
Results – Connectivity Analysis
•b-UEs and r-UEs scattered according to two
homogeneous PPPs with intensity λs=λsu+λsb over a
surface of area |A|, for a set |S| of all terminals
•We assume a b-UE transmits beacons with prob. P
•We consider Rayleigh fading



 g 0 Pt 0 r0

Ps (r0 )  PrSINR     Pr 




  g i Pti ri  

 i





r0  
r0
 
  exp   

Ps  exp   
g
P
r

i
ti
i


Pt 0 
Pt 0 i



 

Noise term
Interf . term
  N 0W
Results – Connectivity Analysis
•Results obtained so far for the proposed D2D
protocol addressed the problem of connectivity
•Aggregate interference at a reference D2D receiver
and after a few tedious computations
•The success probability can be found writing the
Laplace functional with f(x)=exp(-sPtgr-α) in
correspondence of s=θr0α/Pt0

  C 12 /  1  2 /  E 2 / 


r0
i
ps (r0 )  exp   
   exp   sb

Pt 
cos /  


 r0 PI 



Pt 

2 /




•Aggregate interference is modeled with the family of
heavy tailed Stable distributions
Source: M. Z. Win, et al. “A Mathematical Theory of Network Interference and Its Applications,” Proc. IEEE,
vol. 97, no. 2, February, 2009.
Results – Connectivity Analysis
•The connectivity probability in D2D mode Pc is
computed by removing the conditioning on
the number of nodes


pc  1  exp  M 1  e
K  su A  M
N  sb A  (1   ) M
M  NK
 p s p 1  M

su

su  sb
- α=2.1 -α=4 -
Results – Secure Connectivity
D-beacons broadcasting
b-UE
r-UE n
keyring
0001
r-UE 1
keyring
1001
r-UE 3
r-UE 2
keyring
keyring
1100
0100
August 27, 2014
37
Conclusions
•D2D is an emerging wireless technology for direct communications among
devices
•D2D is expected to be a key technology to improve system capacity and
user experience in various scenarios in Beyond 4G/5G technologies
•Public safety is a key driving force for LTE D2D in 3GPP Rel-13
There are several technical issues to be addressed including how to
coexist with cellular users and how to deal with interference
D2D ProSe discovery and communications require fundamental
adaptation to the LTE physical layer (PHY) and radio. It will take a few
years to complete the major changes and another additional time
frame before products are available in the market.
•To leverage all the benefits arising from the adoption of D2D
communications a cognitive mechanism has to be established to
efficiently share the spectrum with cellular communications
QUESTIONS?